Field of the Invention
The present invention relates to a vibration actuator easy in conduction inspection, which brings a vibration element and a driven element into pressure contact with each other and excites vibration in the vibration element to thereby move the vibration element and the driven element relative to each other.
Description of the Related Art
A vibration actuator using an electromechanical energy conversion element represented e.g. by a piezoelectric element uses a friction force acting between a vibration element formed by joining the electromechanical energy conversion element to an elastic body and a driven element, and performs driving for moving the vibration element and the driven element relative to each other. Therefore, the vibration actuator is capable of generating a high thrust or torque in a low-speed region, and has high responsiveness, and hence the vibration actuator can be used as a driving source of a precision instrument without using mechanical transmission means, such as a gear and a belt. Further, when the power is not supplied to the electromechanical energy conversion element, a holding force or a holding torque is generated by friction between the vibration element and the driven element, which eliminates the need of braking means, such as a brake, and therefore, the vibration actuator is applied to a lot of consumer equipment and industrial equipment.
As a vibration actuator, there has been proposed one that forms a vibration element by joining a piezoelectric element to an elastic body made of metal or the like, and applies an AC voltage to the piezoelectric element to excite a specific vibration mode in the vibration element. The vibration actuator applies, for example, two or more AC voltages to the piezoelectric element to generate an elliptic motion on a surface of the elastic body which is in pressure contact with the driven element, thereby causing the vibration element and the driven element to be rotationally or linearly moved relative to each other.
As an example of the vibration actuator, there has been disclosed in Japanese Patent Laid-Open Publication No. 2007-159211 a vibration actuator that uses a vibration element having an annular shape, and an elastic body made of a metallic material having a high resonance sharpness (e.g. a steel material, such as stainless steel) is used in the annular vibration element. To cause the piezoelectric element to generate flexural vibration, such as bending vibration, it is necessary to generate a potential difference in a piezoelectric body (piezoelectric ceramics) as a component of the piezoelectric element. For this reason, in Japanese Patent Laid-Open Publication No. 2007-159211, a GND (ground) portion of the piezoelectric element and the elastic body are electrically connected to each other by a conductive junction made of a conductive material, such as solder, to ground the elastic body, whereby connection of the piezoelectric element to the GND potential is realized by making use of conductivity of the elastic body.
In the case where a conductive material is used for the elastic body, as in the vibration element described in Japanese Patent Laid-Open Publication No. 2007-159211, it is possible to electrically connect the electrode part of the piezoelectric element and the elastic body. However, in some cases, to reduce the cost of the elastic body, the elastic body is formed of a resin material using the injection molding technique which can realize mass production. Further, engineering ceramics are sometimes used for the elastic body for the purpose of improvement of wear resistance.
In a case where the elastic body is formed of a material which is electrically insulating, dielectric, or semi-conductive material, the piezoelectric element cannot be connected to the GND potential via the elastic body. Then, for example, a method is envisaged, in which the piezoelectric body is provided with a through hole, and an electrode formed on a surface of the piezoelectric body, via which surface the piezoelectric body is joined to the elastic body, is drawn to a reverse surface via the through hole. However, the conventional configuration using a through hole has a problem that it is impossible to confirm whether or not sufficient conductivity within the through hole is obtained after the piezoelectric element is joined to the elastic body.